HEAD: default to main for new repositoriesvi-switch-default-ref-main-2

HEAD in bare repositories has the function to determine what the default
reference is. This helps GitLab decide what the target default is for
merge requests and what README to render on the project page.

This change changes the default for new repositories to `main` over
`master`. For almost no-one this would influence their current
repository. There's an exception though; old repositories might have a
corrupt HEAD reference, e.g. it does not exist. In that case Gitaly now
will favour main over master.

Changelog: changed

3 files changed, 35 insertions, 7 deletions

diff --git a/internal/git/repository.go b/internal/git/repository.go
index 76808fc8b..e5f5b25d5 100644
--- a/internal/git/repository.go
+++ b/internal/git/repository.go
@@ -8,13 +8,18 @@ import (
 	"gitlab.com/gitlab-org/gitaly/v14/internal/git/repository"
 )
 
-// DefaultBranch now defaults to master, as that's the Git default
-const DefaultBranch = "master"
+// DefaultBranch is the default reference written to HEAD when a repository is created
+const DefaultBranch = "main"
 
 // DefaultRef is the reference that GitLab will use if HEAD of the bare repository
 // is not found, or other edge cases to detect the default branch.
 var DefaultRef = []byte("refs/heads/" + DefaultBranch)
 
+// LegacyDefaultRef is the reference that used to be the default HEAD of the bare
+// repository. If the default reference is not found, Gitaly will still test the
+// legacy default.
+var LegacyDefaultRef = []byte("refs/heads/master")
+
 var (
 	// ErrReferenceNotFound represents an error when a reference was not
 	// found.
diff --git a/internal/gitaly/service/ref/refs.go b/internal/gitaly/service/ref/refs.go
index 107c469bb..53e5709cb 100644
--- a/internal/gitaly/service/ref/refs.go
+++ b/internal/gitaly/service/ref/refs.go
@@ -241,7 +241,7 @@ func DefaultBranchName(ctx context.Context, repo git.RepositoryExecutor) ([]byte
 		return branches[0], nil
 	}
 
-	hasDefaultRef := false
+	var hasDefaultRef, hasLegacyDefaultRef = false, false
 	headRef, err := headReference(ctx, repo)
 	if err != nil {
 		return nil, err
@@ -256,6 +256,8 @@ func DefaultBranchName(ctx context.Context, repo git.RepositoryExecutor) ([]byte
 		if bytes.Equal(branch, git.DefaultRef) {
 			hasDefaultRef = true
 		}
+
+		hasLegacyDefaultRef = hasLegacyDefaultRef || bytes.Equal(branch, git.LegacyDefaultRef)
 	}
 
 	// Return the default ref if it exists
@@ -263,6 +265,10 @@ func DefaultBranchName(ctx context.Context, repo git.RepositoryExecutor) ([]byte
 		return git.DefaultRef, nil
 	}
 
+	if hasLegacyDefaultRef {
+		return git.LegacyDefaultRef, nil
+	}
+
 	// If all else fails, return the first branch name
 	return branches[0], nil
 }
diff --git a/internal/gitaly/service/ref/refs_test.go b/internal/gitaly/service/ref/refs_test.go
index f07a61e41..f2e3b89da 100644
--- a/internal/gitaly/service/ref/refs_test.go
+++ b/internal/gitaly/service/ref/refs_test.go
@@ -230,7 +230,7 @@ func TestHeadReference(t *testing.T) {
 	headRef, err := headReference(ctx, localrepo.NewTestRepo(t, cfg, repo))
 	require.NoError(t, err)
 
-	require.Equal(t, git.DefaultRef, headRef)
+	require.Equal(t, git.LegacyDefaultRef, headRef)
 }
 
 func TestHeadReferenceWithNonExistingHead(t *testing.T) {
@@ -269,7 +269,7 @@ func TestSetDefaultBranchRef(t *testing.T) {
 		{
 			desc:        "unknown ref",
 			ref:         "refs/heads/non_existent_ref",
-			expectedRef: "refs/heads/master",
+			expectedRef: string(git.LegacyDefaultRef),
 		},
 	}
 
@@ -332,7 +332,7 @@ func TestDefaultBranchName(t *testing.T) {
 		},
 		{
 			desc:     "Get `ref/heads/master` when several branches exist",
-			expected: git.DefaultRef,
+			expected: git.LegacyDefaultRef,
 			findBranchNames: func(context.Context, git.RepositoryExecutor) ([][]byte, error) {
 				return [][]byte{[]byte("refs/heads/foo"), []byte("refs/heads/master"), []byte("refs/heads/bar")}, nil
 			},
@@ -363,9 +363,14 @@ func TestDefaultBranchName(t *testing.T) {
 }
 
 func TestSuccessfulFindDefaultBranchName(t *testing.T) {
-	_, repo, _, client := setupRefService(t)
+	cfg, repo, repoPath, client := setupRefService(t)
 	rpcRequest := &gitalypb.FindDefaultBranchNameRequest{Repository: repo}
 
+	// The testing repository has no main branch, so we create it and update
+	// HEAD to it
+	gittest.Exec(t, cfg, "-C", repoPath, "update-ref", "refs/heads/main", "1a0b36b3cdad1d2ee32457c102a8c0b7056fa863")
+	gittest.Exec(t, cfg, "-C", repoPath, "symbolic-ref", "HEAD", "refs/heads/main")
+
 	ctx, cancel := testhelper.Context()
 	defer cancel()
 	r, err := client.FindDefaultBranchName(ctx, rpcRequest)
@@ -374,6 +379,18 @@ func TestSuccessfulFindDefaultBranchName(t *testing.T) {
 	require.Equal(t, r.GetName(), git.DefaultRef)
 }
 
+func TestSuccessfulFindDefaultBranchNameLegacy(t *testing.T) {
+	_, repo, _, client := setupRefService(t)
+	rpcRequest := &gitalypb.FindDefaultBranchNameRequest{Repository: repo}
+
+	ctx, cancel := testhelper.Context()
+	defer cancel()
+	r, err := client.FindDefaultBranchName(ctx, rpcRequest)
+	require.NoError(t, err)
+
+	require.Equal(t, r.GetName(), git.LegacyDefaultRef)
+}
+
 func TestEmptyFindDefaultBranchNameRequest(t *testing.T) {
 	_, client := setupRefServiceWithoutRepo(t)
 	rpcRequest := &gitalypb.FindDefaultBranchNameRequest{}